Dynamic impact factors of strain hardening UHP-FRC under direct tensile loading at low strain rates

Enhanced matrix packing density and tailored fiber-to-matrix interface bond properties have led to the recent development of ultra-high performance fiber reinforced concrete (UHP-FRC) with improved material tensile performance in terms of strength, ductility and energy absorption capacity. The objective of this research is to experimentally investigate and analyze the uniaxial tensile behavior of UHP-FRC under various strain rates, ranging from 0.0001 to 0.1 1/s. A direct tensile test set up is used. The experimental parameters encompass three types of steel fibers, each in three different volume fractions at four different strain rates resulting in 36 test series. Elastic and strain hardening tensile parameters, such as, cracking stress, elastic and strain hardening modulus, composite tensile strength and strain, energy absorption capacity, and crack spacing of the UHP-FRC specimens, are recorded and analyzed. Explanation of the material’s strain rate sensitivity is mainly based on the inertia effect of matrix micro cracking. Potential contributions of other mechanisms include viscosity of water within nanopores and confinement effects. Dynamic impact factor (DIF) formulas are provided based on the experimental data to illustrate the relationship between DIF and strain rate for UHP-FRC.